The Sasanoa River is about 11 miles in length and connects the Kennebec River at Bath with the Sheepscot River at Westport. The Corps project centers around a 0.5-mile-long stretch of the river at the northeastern end of Arrowsic Island in Arrowsic and south of Woolwich.

Known as Upper Hell Gate, this half-mile stretch was originally constricted by curves and ledges and made more dangerous by swift currents. The Corps’ initial improvement of the waterway, completed in 1898, provided for the removal of various ledge areas, giving the channel a minimum width of 90 feet.

In 1908, the Corps completed additional work in the river. This consisted of widening the channel to a minimum of 140 feet and deepening it to 12 feet by cutting through ledges at Upper Hell Gate and removing Flat Rock to the east. The Corps also removed rock and sunken ledges and built a small jetty on the northeastern side of Arrowsic Island, about 0.5 mile from Upper Hell Gate.

The project has reduced the velocity of the current and allowed larger vessels to make the journey between Bath and Boothbay Harbor via a shorter and more protected route.